AJS & Matchless Owners Club

Hello again. A little problem I discovered last night.

My tank is from India and has a flip type filler cap. All was well until I filled the tank, not to the cap neck but below it. Fuel appears to be seeping through the little breather holes. Is this due to heat either via the paricularly hot spell at the moment or rising heat from the engine?

I made a seal for the cap as it wasn't that brill when I got it and it's providing a fuel tight joint.

Any suggestions would be good however a new tank is not an option!

I've had this happen in very hot weather. After being parked the black tank becomes too hot to touch. My guess is that the petrol is vaporising in the extreme temp inside the tank and condensing as it vents through the breather hole(s). On the other hand, yes, the cap may be leaking

(On a similar note I've had carb icing in high temps (c26 to 36 deg) coupled with with high humidity causing the engine to die. Left for less than a minute the heat of the engine thaws the icing and it restarts but it reoccurs after a few minutes riding).

Had that happen when bikes were new way back in the 50's. The tank needs to breath. It seems in hot weather this is not so easy, as it is also then, I have had fuel cut off due to vacuum. Tank may hiss if you take the top off. I once found mine had almost blocked with polish.

Mine's never blocked from polish, I wonder why.

clive wrote:Mine's never blocked from polish, I wonder why.

That was about 60 years ago Clive.

Thank you for your help and advice. I had seen new fuel caps on ebay but wasn't sure if it was worthwhile getting one. I'll see how she fares through the summer.

I have to fill mine, with a screw down competition type filler, to a level just below the neck, then push down on the filler cap as i tighten it up. Even then I have to take the first few miles very steady to stop any leaks. Breather holes? mine only has one hole and it does not seem to leak from there. I believe it to be an original fitment.
Any ebay new item is likely to be similar quality to your India item. The piecrust type fillers have a little cup type item underneath the breather hole to stop any slopping resulting in leaks there. Might you be able to fabricate something similar for your tank?

clive wrote:I have to fill mine, with a screw down competition type filler, to a level just below the neck, then push down on the filler cap as i tighten it up. Even then I have to take the first few miles very steady to stop any leaks. Breather holes? mine only has one hole and it does not seem to leak from there. I believe it to be an original fitment.
Any ebay new item is likely to be similar quality to your India item. The piecrust type fillers have a little cup type item underneath the breather hole to stop any slopping resulting in leaks there. Might you be able to fabricate something similar for your tank?

Took my screw down comp caps of the CS's as I couldn't stop them leaking when almost full and the staining pee'd me off! I purchased some quality Monza caps and removed the thread as they were screw on and JB welded them on. Spot on now and no more staining

The Monza is probably the way forward but will go on the back boiler for a bit as the tank is freshly painterd

spookefoote1956 wrote:The Monza is probably the way forward but will go on the back boiler for a bit as the tank is freshly painterd

So was mine, I merely masked it all off. Scraped around the filler neck and then glued it on. Neat tidy and no stains.